In recent years, household cogeneration apparatuses and fuel-cell vehicles using solid polymer-type fuel cells have been practicalized and commercialized. Accordingly, research and development of techniques for producing, storing and transporting hydrogen have been activated.
Conventionally known methods for producing hydrogen include, e.g.; a method for separating and recovering hydrogen from coke oven gas; a method for separating and recovering hydrogen from blast furnace gas; a method for separating and recovering hydrogen from naphtha-reformed gas generated in a petroleum refining complex; a method for separating and recovering hydrogen generated from a salt electric field; a method for producing hydrogen by electrolysis of water; and the like. Recently, techniques such as a method for separating and recovering hydrogen from methanol-reformed gas or a method for separating and recovering hydrogen from natural gas and methane-reformed gas have been established and practicalized.
As recent new approaches, a method for producing hydrogen by means of algae using hydrogen fermenting bacteria; a method for producing hydrogen by means of water electrolysis using electric power from solar power generation, wind power generation and small hydroelectric generation; a method for separating and recovering hydrogen obtained by pyrolysis gas of biomass, and the like have been proposed, and some of them have been demonstrated.
As techniques for storing and transporting hydrogen: a method in which hydrogen is charged into a high-pressure gas cylinder, and stored and transported in that state; a method in which an organic solvent such as naphthalene or toluene is hydrogenated (e.g., naphthalene is transported in a form of tetralin, or toluene is transported in a form of methylcyclohexane), and then separated into naphthalene or toluene and hydrogen at each demander so as to utilize hydrogen, and the like have been proposed.
With respect to the method for producing hydrogen as described above, in a method other than water electrolysis, the obtained hydrogen should be separated and recovered from other gas such as carbon dioxide, carbon monoxide, a hydrocarbon gas including methane, or toluene, naphthalene and the like. In addition, a variety of such methods for separating and recovering hydrogen gas from other gas have been proposed.
As a gas separation method for blast furnace gas containing carbon dioxide, nitrogen, hydrogen and carbon monoxide, a pressure swing adsorption-type gas separation method carried out by using a plurality of an adsorption column filled with an adsorbent having a carbon dioxide adsorption capacity higher than each of hydrogen, carbon monoxide and nitrogen absorption capacity and a hydrogen adsorption capacity lower than each of carbon monoxide and nitrogen adsorption capacities, e.g., an active carbon, or for example, a separation method of a blast furnace gas in which mainly carbon dioxide in blast furnace gas is adsorbed into the above-described adsorbent by PSA (Pressure Swing Adsorption) in a high pressure state, and mainly hydrogen is recovered as an unadsorbed gas, has been disclosed (Patent Document 1). In Examples, a separation method using a single-stage PSA with three adsorption columns and an apparatus therefor are used, and thereby carbon dioxide and hydrogen are separated from the blast furnace gas. This method was single-stage style and was carried out at a relatively low pressure of 300 kPa, but hydrogen concentration of the recovered gas was not so high as 60-70%.
A hydrogen producing apparatus has been disclosed comprising: a reforming reaction tube housing a reforming catalyst promoting a reforming reaction for producing hydrogen from hydrocarbons and water, and a carbon dioxide absorbent; a feed unit for feeding a source gas to the reforming reaction tube; a purification unit for separating the reformed gas output from the reforming reaction tube into a product gas with increased concentration of hydrogen and an off-gas with increased concentration of non-hydrogen components; a return unit for returning the off-gas from the purification unit to the feed unit; and a carbon dioxide-withdrawing unit for withdrawing carbon dioxide-rich gas from the reforming reaction tube by depressurizing the reforming reaction tube (Patent Document 2). In this apparatus, carbon dioxide produced by the reforming reaction is adsorbed in the reforming reaction tube, thereby a concentration of carbon dioxide is decreased to increase the concentration of hydrogen in the reformed gas. Thus, there have been necessities that the reforming reaction tube is filled with the carbon dioxide-absorbing material, and the reforming reaction tube is heated to high temperature in order to regenerate the carbon dioxide-absorbing material.
For a hydrogen-producing apparatus in which a hydrogen-containing gas is produced from a hydrocarbon as a raw material by a reformer, the produced hydrogen-containing gas is separated by a hydrogen purification apparatus (PSA) into hydrogen and a concentrated impurity gas containing concentrated gas components other than hydrogen, and the separated hydrogen is recovered as high purity hydrogen, a method for reducing an amount of carbon dioxide emission has been disclosed comprising: burning combustible components in the concentrated impurity gas by a combustion apparatus; and removing carbon dioxide in the combustion gas by a decarbonator (Patent Document 3). Herein, the decarbonator is filled with a carbon dioxide-adsorbing material, e.g., a calcium oxide adsorbent, and carbon dioxide can be adsorbed and removed, but the adsorbed carbon dioxide cannot be reused. In addition, there has been a problem that although the used adsorbent can be reused as a cement solidifying material, it cannot be reused as an adsorbent.
A hydrogen-producing method accompanied with recovery of a liquefied CO2 has been disclosed, comprising: steam-reforming a natural gas fed in a form of liquefied natural gas into a hydrogen-rich reformed gas; separating and purifying hydrogen from this reformed gas; and using off-gas containing combustibles separated in the purification process of hydrogen as a main fuel for combustion and heating in the reforming process, in which method: pure oxygen or highly concentrated oxygen obtained by cryogenic separation using liquefaction cold of liquefied natural gas is introduced as an oxidizer for burning the off-gas in the reforming process; the CO2 gas in the combustion exhaust gas generated in this combustion is concentrated to easily separate and recover the CO2 gas in a liquid state from the combustion exhaust gas; separated and purified hydrogen is pre-cooled by the liquefied natural gas and then cooled and liquefied by liquid nitrogen obtained in the cryogenic air separation; and the liquefied natural gas after used for pre-cooling of hydrogen is utilized to liquefy the CO2 gas and fed to the reforming process of hydrogen (Patent Document 4). There has been a problem that this method utilizes cold generated in vaporizing the liquefied natural gas, and thus the place for using the method is limited.
A hydrogen-producing and carbon dioxide-recovering method for producing hydrogen from carbon-containing fuel and recovering carbon dioxide has been disclosed, comprising: a hydrogen-containing gas producing process, in which the carbon-containing fuel is reformed to obtain the hydrogen-containing gas containing hydrogen and carbon dioxide; a PSA process, in which the hydrogen-containing gas is separated into first hydrogen-rich gas containing enriched hydrogen and PSA off-gas containing enriched components other than hydrogen by means of a pressure swing adsorption apparatus; a carbon dioxide-membrane separation process, in which the PSA off-gas is separated into carbon dioxide-rich gas containing enriched carbon dioxide and carbon dioxide separation membrane off-gas containing enriched components other than carbon dioxide by means of a carbon dioxide separation membrane; and a hydrogen membrane separation process, in which the carbon dioxide separation membrane off-gas is separated into second hydrogen-rich gas containing enriched hydrogen and hydrogen separation membrane off-gas containing enriched components other than hydrogen by means of a hydrogen separation membrane (Patent Document 5). In the method, a separation process by a single-stage PSA and an apparatus therefor are used, and the off-gas discharged from the PSA is further separated into the hydrogen-rich gas and the gas containing the enriched components other than hydrogen by using the carbon dioxide separation membrane and subsequently using the hydrogen separation membrane.